This invention relates to a combination unloader and check valve, and more particularly to an unloader/check valve for use with an air compressor.
The invention especially involves an improvement on an unloader/check valve of the type shown in U.S. Pat. No. 3,358,705, in which the valve is damped to prevent its pulsating in sympathy with the opening and closing of the compressor discharge valves.
Although damped unloader/check valves constructed as shown in U.S. Pat. No. 3,358,705 have given satisfactory service for a long time, certain problems have sometimes arisen. For example, overtightening the threads at the downstream end of the valve sometimes jams the piston of the valve. When the valve is closed, the upstream end of the piston protrudes at the upstream end of the valve and may thereby tend to trap "varnish" and moisture. Also, it may be nicked or otherwise damaged when the valve is installed. With the outer body of the valve made of two threaded-together parts, assembly costs may become relatively high and some misalignment problems may occur.